I'm sure you've checked out Craigslist, but have you checked : http://northerncoloradorentals.com/?
This site has several listings posted by private owners renting their own properties. There are also several property managers: http://www.drakemanor.com/
and many others. Just search for : "property management fort collins"
I typically work on home sales (not rentals) but many of my client need temporary housing or my investors need a place to advertise their properties.
Good luck in your home search.